1. Field of the Invention
The present invention relates to fuel feed mechanism for feeding pelletized fuel from a hopper to the firebox of a stove.
2. Prior Art
In known pellet stoves mechanism is provided for automatically feeding pelletized fuel to the firebox at approximately a uniform, sometimes adjustable, rate. Preferably such stoves are self-feeding for an extended period, such as several hours.
In a positive feed system, the fuel is forcefully moved to the firebox. Known systems use augers or screw conveyors which pulverize some of the fuel pellets and which can become jammed. Another type of positive feed system is shown in U.S. Pat. No. 4,536,120, issued Aug. 20, 1985, to Kylmanen et al. and U.S. Pat. No. 4,474,117, issued Oct. 2, 1984, to Marollaud. In the device of each of those patents, a piston is reciprocated horizontally below the bottom outlet opening of a hopper to move pelletized fuel from the hopper along a feed cylinder or trough. In the piston feeder of the Marollaud patent, the piston is stated to form a "fire barrier" in its "rest position". See the paragraph beginning a column 2, line 38 and the first three paragraphs of column 4.
As an alternative to a positive feed system, one known system uses a rotating tube inclined downward from the bottom of a hopper to a chute leading to the firebox. Fuel pellets are tumbled in the tube and slide and roll downward along it to the chute. See the brochure titled "The Inside Story on the Most Significant Improvements in Pellet Stove Technology" concerning pellet stoves sold under the trademark "Eclipse" by Horizon Research, Inc., of Bothell, Wash.
Other types of "passive" feed systems which have been used for coal burning stoves or boilers are shown in the following U.S. patents:
U.S. Pat. No. 701,192, issued May 27, 1902 (Fraser); PA0 U.S. Pat. No. 1,442,295, issued Jan. 16, 1923 (Porter); PA0 U.S. Pat. No. 1,942,947, issued Jan. 9, 1934 (Strange); PA0 U.S. Pat. No. 2,078,640, issued Apr. 27, 1937 (Segar); PA0 U.S. Pat. No. 2,204,555, issued Jun. 18, 1940 (Valentine et al.); PA0 U.S. Pat. No. 4,537,140, issued Aug. 27, 1985 (Baker); PA0 U.S. Pat. No. 4,328,786, issued May 11, 1982 (Owen).
In the feed mechanism of each of the above devices, lumps of coal are fed to a firebox by reciprocating, oscillating or vibratory motion of a feed plate or trough positioned below the bottom outlet of a hopper.
In the passive feed devices, there can be a danger that the fire will spread along the feed trough or plate, possibly to the hopper.